[Aroid-l] Tubers, corms and bulbs, oh my!

From: ExoticRainforest <Steve at exoticrainforest.com> on 2010.02.13 at 21:02:20 Thanks Dylan!  I have been trying to do a fair amount of research to better understandall these terms for the past 6 weeks.  I corresponded with Wilbert afew months ago and helped a great deal to make the subject clearer. Tom also sent a number of corrections to some of my personalmisunderstandings  so thanks to both of you along with Christopher andTom for all these very clear explanations. By the way Dylan, the IAS is growing and we need more authoritativevoices on Aroid l..  Thanks a bunch for making your firstcontributions, please don't make it your last!  All of us need good info rather than much of the mishmash found on theinternet.  I'm certain the IAS board will back me up in thanking you,Tom, Wilbert, Pete, Eduardo, David, Simon, Marcus, Marc, Julius and allthe authoritative voices that make sure we read good info!  The nextissue of the IAS Newsletter will be out in about one month so if any ofyou on Aroid l haven't joined please take the time to do it now.  www.Aroid.org By the way, I haven't read any responses to Ted Held's post regardinghearing some of Julius' personal stories.  If you missed that post youcan find it here:  http://www.hort.net/lists/aroid-l/feb10/msg00020.html I have already listened to his narration about Christmas dinner inTrinidad and strongly suggest all of you that have read Julius' greatposts but never had the pleasure of hearing his voice visit the site! It is a riot, and that does not count for the fact our old Aroid l friend is incredibly brilliant! Thanks again! Steve Lucas www.ExoticRainforest.com Hannon wrote: Thanks to Wilbert for a very good synopsis of 'compact rootstocks' ortubers in Araceae. As a first time Aroid-Ler and longtime aroider Iwould like to offer a few comments.I think what Wilbert elaborates here makes perfect sense. My onlyquibble is that if we make no use of existing descriptive terminologythen we use more words than we need to to describe things, or we usewords that have imprecise or vague meanings. If all these structuresare rhizomes or (apparently) derived evolutionarily from rhizomes,that is very useful as a concept. Yet within this scheme there arestructures that can be differentiated, if arbitrarily, into morenarrowly defined notions such as tubers, rhizomes and corms.Some of us are weary of any confining definitions altogether. In thecase of rootstocks especially it is difficult to imagine any taxonomythat could capture and discretely name the different types found innature. In fact it has not been done. Still, it seems to me that acorm is something quite distinct, even if its origins are betrayed bypeculiar congeners, as in Wilbert's Amorphophallus example. Anymodular unit that may resemble a tuber or bulb and _replaces itselfeach growing season_ can rightfully be called a corm, regardless ofthe number of nodes/internodes involved or features of tunics vs.naked flesh. Annual replacement is the key trait of a corm.Other families exhibiting "true" corms that are replaced annually(sources in the botanical literature give inconsistent definitions)are the iris family (Gladiolus, Crocus, etc.), Themidaceae (Brodiaea,Milla, etc.) and some Cyanastraceae/Tecophilaeaceae. "Chains oftubers" can be found in Dierama and probably others and perhapssimilar ontogenic processes have been at work in these families. Asfar as I know the rootstocks of these plants have traditionally, inbotany, been labeled "corm" and not tuber or bulb. This concisedesignation continues to serve a useful purpose for the scientist andlayman alike. As Wilbert indicates, we have "traditionally" called thetuber-like structures in aroids, well, tubers.If we say there is only a morphological continuum, or that all therootstock types in a group are basically rhizomes, then clarificationand elucidation are sacrificed.Dylan Hannon --------------000501020207090908050008

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